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In a paper published in the Geological Magazine, September, 1894, Sir Henry Howorth expatiates on recent changes of the relative level of land and sea in support of his views on the Mammoth age and his diluvial catastrophe,inwhich there seems to me some very extraordinary confusion in the matter of geological chronology and sequence of events. The first paragraph reads as follows:—“In some recent papers published in the Geological Magazine, I have endeavoured to show that at the close of the Mammoth age there was a very considerable dislocation of the Earth's crust, and that a consequence of it was the upheaval of Some of the highest masses of land on the earth, including the massive mountains of Asia and the American Cordillera. I now propose to show that (as is a priori probable) there was a concurrent collapse or sinking of the ground over large areas, which, as in the corresponding upheaval, was very rapid, if not sudden” (the italics are mine). The suggested relationship of these various events and their alleged catastrophic character, induces me to again enter this ever-expanding field of controversy.In support of his thesis Sir Henry first refers to the subsidences which resulted in the separation of England from the Continent, and consequent extinction of the Mammoth. Assuming that the course of things was as stated, when it is further suggested that this event was contemporaneous with great dislocation of the Earth's crust, resultinginstupendous upheavals of mountain ranges in Asia and America, he attempts more than can well be proved.

Mr. Hills’s paper suggests a number of questions, some of which can be fairly definitely answered, while others seem to me to be worth recording on the principle that the best way to get a question answered is to ask it. The separation of the granitic material into limited regions of the earth’s surface to form the continents could clearly not occur when the earth was fluid, and after the earth solidified any mechanical cause would meet formidable difficulties. Explanations seem to be restricted to (1) a failure or partial failure of magmatic differentiation in the oceanic regions, so that the granite has separated out since solidification in the continental regions, but remained dissolved in the oceanic ones, (2) some mechanical process arising during solidification. There are difficulties about both possibilities. Mr. Hills’s theory belongs to the second class, and I think needs serious consideration.

While giving ample credit to Mr. R. Mallet for the ingenuity displayed in his novel suggestion as to the cause of volcanic energy (or Vulcanicity, as he calls it), and for the elaborate experiments and calculations which he brings to its support, Geologists have some reason to complain of the supercilious tone in which he notices, only to throw them aside as unworthy of notice, the theories of all preceding writers on the same subject, who have expressed views differing from that which he adopts. It is needless to give instances of this tone which pervades the whole paper, and must strike every one who reads it.

From a long and careful study of the Brachiopoda I am led to offer some observations upon the two recently published papers by Dr. J. Allan Thomson which have appeared in this Magazine. In the case of Dallina I cannot agree with Dr. Thomson regarding the type of folding. He considers D. septigera (the genotype) and D. raphaelis as dorsally biplicate, D. floridana as dorsally uniplicate. Now dorsal biplication is brought about by the dorsal sulcus being superimposed upon a single dorsal fold. In D. septigera, as well as in D. floridana, a broad ventral sulcus is superimposed upon a dominant ventral fold; these two species, therefore, are, in my opinion, ventrally biplicate (as in Magellania flavescens and some others).

The question of the supposed isostatic adjustment of the earth's crust to increase or decrease of load has recently come prominently to the fore in connexion with the Wegener hypothesis and Joly's theory of geological transgression and revolution. The principle itself is fairly well established by several independent lines of evidence, but there is room for clearer thinking as to the mechanism attending its operation. Very varied opinions are for instance held as to therapidity and completeness of the adjustment, and unjustifiable assumptions are made with regard to the displacement of magma beneath depressed areas. It is very necessary to keep an open mind on these questions and to search the available evidence for means of defining the nature of the attendant sub-crustal movements.

The suggestion that the Skye amygdaloidal gabbro represents amygdaloidal basaltic lava in which the grain-size has been coarsened by recrystallization does not imply “an unusual type of metamorphism” as Bailey supposes. Whereas recent lava-flows are fine-grained, older flows, particularly pre-historic examples, commonly have a doleritic or gabbroic grain-Size. Bore-hole investigations in Yellowstone Park indicate that such increase in grain-size is a consequence of the long-continued through-passage of gases and water escaping to the surface. Bailey's own observation that amygdales within the Skye amygdaloidal gabbro “interrupt the form of the bigger feldspars” provides evidence that the bigger feldspars are younger than the amygdales, and that the rocks containing them have therefore recrystallized

The above paper, read before the Geological Society on the 27th May last, having just reached my hands, with the discussion, I trust you willallow me to make some observations thereon, not having been present on the occasion. As my name does not appear once throughout the paper it might at first sight be considered unnecessary, if not impertinent, for me to take any direct notice of its contents. I must therefore ask permission to state the reasons for this communication as briefly as may be, and they may be summed up in a single sentence—that, being responsible as the officer of the Survey who carried out the geological mapping of the Cotteswold Hills and of the outlying Bredon Hill, I cannot allow reflections on its accuracy to pass unanswered.

MR. Bailey has very kindly permitted me to see his manuscript, and also to examine a specimen and slice of the rock which he regards as a volcanic breccia underlying the pitchstone. Since he attaches some importance to this rock, I will consider it first.The natural base of the thick pitchstone sheet is made by a band of more glassy aspect, almost like an obsidian. The microscope shows that this, apart from the usual enclosed crystals, is a light-brown glass, free from the crowds of crystallites found in the ordinary pitchstone. Another feature is that it encloses numerous little fragments of basalt. These indeed, with occasional larger pieces, pass up for some feet into the pitchstone, but they are most abundant near the lower surface. Such inclusions, picked up from the contiguous rocks, may occur both in lava-flows and intrusive sills, but, so far as my experience goes, are more frequent in the latter. The obsidian-like band is well seen, fresh and intact, at places on the northern side of the SgÙrr; but elsewhere it is much brecciated, and usually much decomposed in addition. The brecciation is of such a kind that pieces of the normal pitchstone have become mingled with the debris of the more glassy variety. Mr. Bailey has quoted part of my description of this brecciated basal band as it is exposed, in a decomposed state, on the southern side of the ridge. That it is a part of the pitchstone sheet, not a separate underlying deposit, is there clearly demonstrated: see fig. 6 on p. 60 of my paper.

I Have been very much interested in reading Mr. Russell's two communications published in the Geological Magazine for August and September last. The analogy which he draws between the history of the Dead Sea valley and that of some of the lake valleys in the western part of North America is instructive as showing how similar physical features can be accounted for on similar principles of interpretation over all parts of the world. Mr. Eussell very properly draws attention to the paper by his colleague Mr. G. K. Gilbert on “The Topographical Features of Lake Shores,” in which principles of interpretation of physical phenomena are laid down applicable to lakes both of America and the Jordan-Arabah valley. With some of Mr. Russell's inferences regarding special epochs in the history of this valley I am very much disposed to agree; more particularly in reference to the mode of formation of the Salt Mountain, Jebel Usdum; or rather, of the salt-rock which forms the lower part of its mass. If this interpretation be correct, it removes the difficulty of understanding why the rock-salt is confined to one small corner of the lake, which, at the time the salt was in course of formation, was vastly more extensive than at present.

When I sent the above paper to the Geological Magazine, I was not aware that a Sketch of the Geology of the Isle of Man, by Mr. John Home, F.G.S., of the Geological Survey of Scotland, had been published in the Transactions of the Edinburgh Geological Society.